Vintage fender sidekick tube 20r 1986 model burnt resistors! R57 R58

[g1]

If it specifies 100V operation, it must have been originally from Japan.
Did you try measuring the resistance of those resistors you removed?

[teemuk]

...And if you sketch out the circuit(s) from which those resistors are from it might help to determine their component values. If not exactly, then at least a close-enough values.

Sometimes you simply have to live with the fact that no technical documentation is available. It's a basic mid 1980's amp design, how hard can it be?

They seem to be in close vicinity to power supply circuit and what looks like either power amp or a regulator IC. Part of the regulator or voltage dropping circuit of the supply perhaps? What is the power amp or regulator IC, and could its datasheet perhaps provide some clues about involved circuitry? Where are the circuit board tracks running from those resistors?
Do you -really- need a schematic for this? I understand it can be a convenience but for fixing this thing... do you really need it?

[g1]

It's good that Teemu mentioned these being from the same origin as the R.A.D. & H.O.T. Those schematics are available.

neilemborgo7, are there numbers on the power transformer that can help us match this up to another schematic?

[J M Fahey]

Well a search turns up no schematic for the 20r but we get the 15, 25, 35, 65 here https://music-electronics-forum.com/...ad.php?t=33010
nosaj

It's good that Teemu mentioned these being from the same origin as the R.A.D. & H.O.T. Those schematics are available.

Sadly none of those applies.
Those are all transistor amps, while this one is the very odd TUBE one.

So unusual that I didnīt know they even *existed* , go figure.

Did anybody actually read thread title and look at amp picture?

[nosaj]

Can you give us a pic of the whole PCB and the back side of the amp please?

Thanks,
nosaj

[g1]

Sadly none of those applies.
Those are all transistor amps, while this one is the very odd TUBE one.

So unusual that I didnīt know they even *existed* , go figure.

Did anybody actually read thread title and look at amp picture?

I looked at it, and the board pics. I could only see a preamp tube socket so I figured maybe it just has a single preamp tube. Regardless, the burnt resistors are around a couple zeners and typical +/-15V rail size caps, so I figured the LV supplies might be the same.
But you have a good point, the transformer won't match any of the others because it will have a HV winding.

[nosaj]

I looked at it, and the board pics. I could only see a preamp tube socket so I figured maybe it just has a single preamp tube. Regardless, the burnt resistors are around a couple zeners and typical +/-15V rail size caps, so I figured the LV supplies might be the same.
But you have a good point, the transformer won't match any of the others because it will have a HV winding.

only close thing I can find and no schematic. is the sidekick tube 30r 2 preamp tubes and a solidstate rearend.https://www.radiomuseum.org/r/fender..._tube_30r.html
nosaj

[J M Fahey]

only close thing I can find and no schematic. is the sidekick tube 30r 2 preamp tubes and a solidstate rearend.https://www.radiomuseum.org/r/fender..._tube_30r.html
nosaj

Interesting.
Letīs wait for a few closeups covering the full amp to start guessing with at least some data.

What I find REAL weird is that power IC shown not only is not attached to a heat sink, but it works as heat sink for a TO220 transistor

[Jazz P Bass]

That output IC may be the HA1388.
HA1388.pdf

Here is a crop of the 25R power supply.
Sidekick 25 Reverb Pwr Supply.pdf
Particularly the 15 Vdc supply.
It shouldn't be that different.

[neilemborgo7]

https://drive.google.com/drive/folde...GtWTc95ImPo0az

Sorry for this very late reply. Here some more pics of the amp. I hope you can help me.

[The Dude]

......Did you try measuring the resistance of those resistors you removed?

^^^^^^ I'll go back to this. Often resistors darken, but don't change value much. Measurements might at least get us in the ballpark.